The present invention relates to a thermoplastic elastomer composition having excellent heat aging characteristics, weather resistance, low-temperature physical properties, oil resistance and flexibility, and to moldings using the same.
Hoses comprising an inner tube, a reinforcing layer and an outer tube annularly laminated in this order are known. In those hoses, the inner tube and the outer tube are constituted of a rubber such as vulcanized rubbers and polyurethane, or a resin such as polyesters and nylons; the reinforcing layer is braided in a braid or spiral form with fibers such as nylons, polyesters, rayon, vinylon and aramid fibers; and the respective spaces between the layers are subjected to adhesion treatment with, for example, a rubber cement or a urethane-based adhesive. However, since production of so-called rubber hoses in which the inner and outer tubes are made of a rubber requires a vulcanization step, the production steps thereof become complicated so that the production cost is inevitably high. Further, so-called resin hoses in which the inner and outer tubes are merely made of a thermoplastic resin involve problems such that the hose is hard and poor in flexibility so that when it is bent, kink phenomenon occurs. In order to overcome those problems, a hose using a thermoplastic elastomer composition in which a vulcanized rubber phase, at least a part of which is crosslinked, is dispersed in a thermoplastic resin such as olefin thermoplastic resins, vinyl chloride-based thermoplastic resins, aramid-based thermoplastic resins and ester-based thermoplastic resins is proposed as disclosed in, for example, JP 6-64102A. However, considering from the standpoint of oil-resistant hoses, since general olefin thermoplastic elastomer compositions comprise polypropylene and an ethylene-propylene-based rubber and do not contain a polar group in the molecular structures thereof, they have a disadvantage to be poor in oil resistance. On the other hand, in order to improve the oil resistance, a thermoplastic elastomer comprising polypropylene and an acrylonitrile-butadiene-based rubber, and a thennoplastic elastomer comprising an ethylene-acrylic acid ester copolymer rubber and a polyolefin are proposed. However, although the former has excellent oil resistance, it contains a double bond in the molecular structure thereof. This involves the problem that the composition is poor in heat resistance and weather resistance. Further, although the latter has excellent heat resistance and weather resistance, it contains an ethylene moiety in the molecular structure thereof. This involves the problem that the composition is still poor in oil resistance, and particularly, the composition cannot substantially be used for fuel oils. A three-components blend comprising polypropylene, an acrylonitrile-butadiene-based rubber and an ethylene-acrylic acid ester rubber is proposed as a compromise of those compositions. However, this three-components blend was insufficient in a balance between heat resistance and oil resistance.
Accordingly, one object of the present invention is to provide a thermoplastic elastomer composition having excellent heat aging characteristics, weather resistance, low-temperature physical properties, oil resistance and flexibility.
Another object of the present invention is to provide moldings using the composition.
As a result of extensive and intensive investigations to achieve the above objects, it has been found that a thermoplastic elastomer composition having excellent heat aging characteristics, weather resistance, low-temperature physical properties, oil resistance and flexibility can be obtained by dynamically heat treating a mixture comprising (A) an olefin resin, (B) a specific acrylic rubber and (D) an inorganic filler in the presence of (E) a crosslinking agent. The present invention has been completed based on this finding.
The present invention provides a thermoplastic elastomer composition obtained by dynamically heat treating a mixture comprising (A) an olefin resin, (B) an unsaturated group-containing acrylic rubber and (D) an inorganic filler in the presence of (E) a crosslinking agent, wherein the component (B) comprises:
(B1) from 55 to 94.99% by weight of a structural unit derived from an acrylic acid alkyl ester monomer and/or an acrylic acid alkoxyalkyl ester monomer,
(B2) from 0.01 to 20% by weight of a structural unit derived from a monomer having a carbon-carbon double bond in a side chain thereof,
(B3) from 5 to 30% by weight of a structural unit derived from an unsaturated acrylonitrile monomer, and
(B4) from 0 to 30% by weight of a structural unit derived from a monomer copolymerizable with (B1), (B2) and (B3), provided that the sum of (B1), (B2), (B3) and (B4) is 100% by weight.
The present invention further provides moldings using the above thermoplastic elastomer composition.
The moldings are preferably a hose.